Re: [RFCv2 22/37] KVM: s390: protvirt: handle secure guest prefix pages

[David Hildenbrand <david@redhat.com>]

On 03.02.20 14:19, Christian Borntraeger wrote:
> From: Janosch Frank <frankja@linux.ibm.com>
> 
> The SPX instruction is handled by the ulravisor. We do get a
> notification intercept, though. Let us update our internal view.
> 
> In addition to that, when the guest prefix page is not secure, an
> intercept 112 (0x70) is indicated.  To avoid this for the most common
> cases, we can make the guest prefix page protected whenever we pin it.
> We have to deal with 112 nevertheless, e.g. when some host code triggers
> an export (e.g. qemu dump guest memory). We can simply re-run the
> pinning logic by doing a no-op prefix change.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  arch/s390/include/asm/kvm_host.h |  1 +
>  arch/s390/kvm/intercept.c        | 15 +++++++++++++++
>  arch/s390/kvm/kvm-s390.c         | 14 ++++++++++++++
>  3 files changed, 30 insertions(+)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 48f382680755..686b00ced55b 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -225,6 +225,7 @@ struct kvm_s390_sie_block {
>  #define ICPT_PV_INT_EN	0x64
>  #define ICPT_PV_INSTR	0x68
>  #define ICPT_PV_NOTIF	0x6c
> +#define ICPT_PV_PREF	0x70
>  	__u8	icptcode;		/* 0x0050 */
>  	__u8	icptstatus;		/* 0x0051 */
>  	__u16	ihcpu;			/* 0x0052 */
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index d63f9cf10360..ceba0abb1900 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -451,6 +451,15 @@ static int handle_operexc(struct kvm_vcpu *vcpu)
>  	return kvm_s390_inject_program_int(vcpu, PGM_OPERATION);
>  }
>  
> +static int handle_pv_spx(struct kvm_vcpu *vcpu)
> +{
> +	u32 pref = *(u32 *)vcpu->arch.sie_block->sidad;
> +
> +	kvm_s390_set_prefix(vcpu, pref);
> +	trace_kvm_s390_handle_prefix(vcpu, 1, pref);
> +	return 0;
> +}
> +
>  static int handle_pv_sclp(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_s390_float_interrupt *fi = &vcpu->kvm->arch.float_int;
> @@ -475,6 +484,8 @@ static int handle_pv_sclp(struct kvm_vcpu *vcpu)
>  
>  static int handle_pv_not(struct kvm_vcpu *vcpu)
>  {
> +	if (vcpu->arch.sie_block->ipa == 0xb210)
> +		return handle_pv_spx(vcpu);
>  	if (vcpu->arch.sie_block->ipa == 0xb220)
>  		return handle_pv_sclp(vcpu);
>  
> @@ -533,6 +544,10 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
>  	case ICPT_PV_NOTIF:
>  		rc = handle_pv_not(vcpu);
>  		break;
> +	case ICPT_PV_PREF:
> +		rc = 0;
> +		kvm_s390_set_prefix(vcpu, kvm_s390_get_prefix(vcpu));

/me confused

This is the "request to map prefix" case, right?

I'd *really* prefer to have a comment and a manual

/* request to convert and pin the prefix pages again */
kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu)

A TLB flush is IMHO not necessary, as the prefix did not change.

> +		break;
>  	default:
>  		return -EOPNOTSUPP;
>  	}
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 76303b0f1226..6e74c7afae3a 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3675,6 +3675,20 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
>  		rc = gmap_mprotect_notify(vcpu->arch.gmap,
>  					  kvm_s390_get_prefix(vcpu),
>  					  PAGE_SIZE * 2, PROT_WRITE);
> +		if (!rc && kvm_s390_pv_is_protected(vcpu->kvm)) {
> +			do {
> +				rc = uv_convert_to_secure(
> +						vcpu->arch.gmap,
> +						kvm_s390_get_prefix(vcpu));
> +			} while (rc == -EAGAIN);
> +			WARN_ONCE(rc, "Error while importing first prefix page. rc %d", rc);
> +			do {
> +				rc = uv_convert_to_secure(
> +						vcpu->arch.gmap,
> +						kvm_s390_get_prefix(vcpu) + PAGE_SIZE);
> +			} while (rc == -EAGAIN);
> +			WARN_ONCE(rc, "Error while importing second prefix page. rc %d", rc);

Maybe factor that out into a separate function (e.g., for a single page
and call that twice).

> +		}
>  		if (rc) {
>  			kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
>  			return rc;
> 


-- 
Thanks,

David / dhildenb